a few Ideas I had for boss monsters in my Archtype "Nightshade" each has 3 forms

Nightshade, Gravity Dragon
Wyrm/Xyz/effect
3 level 3 "nightshade" monsters
once per turn, you can detach 1 Xyz material from this card to target 1 card on the field, set that card face-down. cards set face-down by this cards effect cannot be flipped face-up until your opponents next end phase. if this card would be destroyed while it has no xyz materials, send it to the Extra deck instead.
1500 ATK 300 def

Nightshade, Supreme Gravity Dragon
Wyrm/Xyz/effect
2 level 6 "nightshade" monsters
when this card is Xyz summoned, select either your opponents monster zone or spell/trap zone, set all cards in your selected zone.
if this card has a "Nightshade, Gravity Dragon" attached to this card as Xyz materials, you can detach 2 xyz materials to activate one of these effects.
-If your opponent has only face-down monsters on their field, this card can attack your opponent Directly, but battle damage is halved.
-Target up to 3 Face-down cards on the field, as long as this card is on the field, the selected cards cannot be flipped face-up.
2300 atk 1900 def

Nightshade, Uber Gravity Dragon
Wyrm/Xyz/Effect
2 Rank 9 "Nightshade" Xyz monsters
When this card is Xyz summoned, set all other cards on the field, cards set by this effect cannot be flipped face-up until the endphase.
you can detach 3 Xyz materials from this card to have this card be able to attack your opponent Directly this turn, damage is halved from all battles this turn.
you must detach 3 Xyz Materials, and send the top 20 cards of your deck to the grave to declare an attack with this card, cards sent to the grave by this effect cannot activate their effects in the grave.
if this card has 2 or less Xyz materials during the end phase, banish it, then special summon 1 "nightshade, Gravity dragon" from your extra deck or grave.
5000 atk 0 def

Nightshade, Holy Cherub
Fairy/Synchro/Effect
1 "Nightshade" Tuner + 1 or more non-tuner monsters
this card can be synchro summoned even if you cannot special summon. when this card is Synchro summoned, you can return 1 face-up trap and 1 monster from the field to the hand. if this card is sent to the grave, you can special summon the materials used for the synchro summon of this card, you can only summon 1 "Nightshade, Holy Cherub" per turn.
0 attack 0 def

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